This invention relates to the art of press tooling and, more particularly, to a load equalizing arrangement for plural press tools.
It is often desirable to provide a single press with plural sets of opposed tools to enable a number of pressing operations to be achieved simultaneously during each working stroke of the press. Such tool sets may, for example, be defined by opposed sheet metal shaping dies, opposed punch and die components, and the like, and the plural pressing operations performed thereby may either be like or different with respect to the work performed by the tooling. In any event, a difference in workpiece thickness from that for which the tools are adjusted results in undesirable eccentric loading of the press slide and frame upon engagement of the tooling with the workpieces. This is especially true where the press slide is of the single point drive type in which the driving force is through a single axis centrally of the slide and the press tools are laterally spaced from the slide axis. In this respect, if one tool pair engages a workpiece therebetween before the other tool pair, the working force is transmitted axially of the first tool pair while the other tool pair is unloaded. Thus, the slide is eccentrically loaded due to the spacing of the tooling from the slide axis, and this load is transmitted by the slide to the press frame resulting in severe wear of the slide guides and possibly failure of the guides and press frame. Moreover, such wear of the slide guides leads to inaccuracy with respect to lateral positioning of the slide and thus inaccuracy with respect to cooperative interengagement between the opposed tool components. These problems often make it impractical to perform plural press operations simultaneously in a single point mechanical or hydraulic press.
Such eccentric loading can be avoided by mounting multiple tools on the press for axial displacement relative to one another, such as shown in U.S. Pat. No. 1,937,908 to O'Brien, so that a working force is not applied until all of the tools engage corresponding workpiece portions. Such relative tool displacement alone, however, introduces undesirable limitations on the use of a press for performing sequential working operations on a given workpiece at multiple working stations of a press and/or performing different working operations on a given workpiece at a single working station of a press. In this respect, once the tools are relatively positioned during engagement thereof with a workpiece, such positioning is maintained during the subsequent return and work stroke of the press. In a press wherein a workpiece is advanced step-by-step to sequential tooling stations for the sequential performance of different work thereon, such initial tool positioning can result in interference between the workpiece and tooling during workpiece transfer and/or between the tooling and the workpiece feed mechanism during the workpiece transfer, thus subjecting the tooling, workpiece and transfer mechanism to potential damage. While these problems might be avoided in connection with a press having a slide stroke sufficiently long to assure necessary workpiece-tool and tool-feed mechanism clearances, it will be appreciated that such a requirement not only limits use of the tooling arrangement to certain presses but additionally results in inefficient press operation and limits the versatility of both the tooling and presses with which the tooling might otherwise be used.
Further in the foregoing respect, it is often desired to provide a press with a plurality of work stations each capable of performing the same working operation on a given workpiece using alternately available like tools on one of the press slide and bed members, or sequentially performing different tooling operations by alternately available different tools on the press member. More particularly, in hot forming a plurality of workpieces at different work stations of a press, shuttle mechanisms are often provided for sequentially presenting cooled tooling on successive strokes of the slide to enable the tooling just used to cool or be cooled. This enables operating the press at an efficient stroke rate. Similarly, tool shuttles are often provided to sequentially position functionally different tooling at a given work station during succeeding slide strokes for different working operations to be performed on a given workpiece at the work station. Often, such shuttling mechanisms require predetermined positioning of tools relative thereto to enable operation of the shuttle. Thus, relative load equalizing positioning of tooling during one stroke of such a press tooling arrangement, without more, could cause inoperability of the shuttle mechanism. Even if such inoperability is not a problem, it remains that such relative positioning can result in tool-workpiece and/or tool-feed mechanism interference and/or damage which as mentioned above can be avoided only by limiting use of such tooling to a press having sufficient stroke length to assure clearances to avoid such interference.